New human ancestor walked and climbed 3.4 million years ago in Lucy's time, Cleveland team finds (video)

View full sizeLisa DeJong, The Plain DealerA plaster cast of the Burtele forefoot fossils on the left shows the grasping, apelike big toe. In the modern human foot, right, evolutionary changes have moved the big toe in line with the others, allowing for the development of a shock-absorbing arch for long-distance walking.

CLEVELAND, Ohio -- Lucy didn't walk alone.

A second type of early human ancestor could stand and stride on two legs, occasionally sharing the ground with the iconic, upright-walking Lucy and her kin 3.4 million years ago in the river deltas of eastern Africa, a Cleveland-led research team revealed Wednesday.

But unlike the highly mobile Lucy, the newly discovered creature wasn't fully committed to life out of the trees.

The eight fossilized foot bones that scientists from the Cleveland Museum of Natural History and Case Western Reserve University unearthed in the Ethiopian badlands and analyzed for the past three years come from a more primitive foot than Lucy's species, Australopithecus afarensis. The forefoot is still primarily equipped for tree-climbing, though it would have allowed short-distance travel on the ground.

The discovery further illuminates bipedality's diverse origins, and the critical, sometimes circuitous evolutionary changes the human foot had to undergo to support modern walking.

View full sizeCourtesy Yohannes Haile-Selassie, Cleveland Musuem of Natural HistoryYohannes Haile-Selassie, the Cleveland Museum of Natural History's curator of physical anthropology, examines a fossil in the Afar region of Ethiopia.

"Obviously, the nature of our evolution is more complicated than we think," Yohannes Haile-Selassie, the Cleveland museum's physical anthropology curator and the study's lead author, said in a telephone interview from Addis Ababa, where he announced the discovery Wednesday.

"Definitely, there were two different pre-human species roaming around at 3.4 million years ago in the same area," he said. "What this tells you is that a species didn't have to be fully bipedal to exist," even after Lucy and her kin had mastered the shift to life on two legs.

Lucy's foot is anatomically like ours, meaning she could walk almost as well as today's humans. The newly discovered partial right foot, which belonged to an as-yet unclassified adult hominin, or human ancestor, has a mix of features, the researchers report in this week's edition of the journal Nature. Some elements are monkey- and ape-like, and some are human. The creature's four smaller toes show the ability to bend and push off the ground at the start of a step. But the big toe is sideways-pointing, like an ape's – a powerful "opposable" gasping pincer that would have made the creature an excellent tree-climber, but an awkward, short-distance ground-traveler.

Cleveland Museum of Natural History announces new hominid speciesFossilized foot bones, unearthed by scientists from the Afar region of Ethiopian two years ago, have been analyzed by scientists from the Cleveland Museum of Natural History and Case Western Reserve University in Cleveland. The research team announced today that it had concluded that the fossils are the remnant of a second type of early human ancestor that walked alongside the iconic "Lucy" about 3.4 million years ago.

Previously, many scientists had thought the able-walking Lucy and her kind were the only hominin species living between 3 million and 4 million years ago, and that bipedality – humanity's defining trait – was firmly established by then.

The Cleveland team's surprising find shows that Lucy's species wasn't alone, and that at least two forms of two-legged locomotion – one a harbinger of the future and the other an apparent holdover from the past – coexisted side by side for a time, like a Prius and an oxcart on the same roadway.

"Afarensis had given up the trees and went fully terrestrial," said CWRU anatomy professor and former natural history museum director Bruce Latimer, a co-author of the report. The creature whose forefoot bones the team discovered "is probably not coming down very often. This guy would have been up in the trees and Lucy would have been staring at it."

View full sizeLisa DeJong, The Plain Dealer"This is one of those things you see and it takes you by surprise," study co-author Bruce Latimer says of the mixture of primitive and modern elements in the Burtele forefoot. Latimer is a Case Western Reserve University anatomy professor and a professor in the CWRU dental school's department of orthodontics.

The partial foot fossils were found in an area called Burtele (pronounced Bur-TEH-lay) about 30 miles north of the site where another Cleveland Museum of Natural History team discovered Lucy's skeleton in 1974. Though Lucy's ground-dwelling species and its tree-preferring Burtele counterpart would have occupied different habitats, it's possible they crossed paths, Haile-Selassie said.

While such encounters may seem strange to we Homo sapiens – a species used to its singularity on the planet – they were a fact of life to our ancestors in the distant past.

"We think humans are superior and we can only imagine there being one of us," said University of Missouri paleoanthropologist Carol Ward, an expert on early human evolution who was not involved in the partial foot discovery.

"If we take off our human goggles and put on our ape goggles, we can see and appreciate and accept more diversity," she said."We have chimps and gorillas living in the same forest together today. For all practical purposes, these [early human ancestors] were bipedal apes. That may be what we're looking at here, that there are at least a couple of different ways to be an early hominin," a development Ward called "exciting."

Haile-Selassie and Latimer, the co-directors of the expedition that recovered the foot bones, are veteran fossil hunters who've been involved in some of the most significant human evolutionary finds of the last quarter-century.

View full sizeAssociated PressThe partial skeleton of Lucy and other fossils from her species, Australopithecus afarensis, show anatomical adaptations that allowed modern-style upright walking.

As a graduate student in the 1970s, Latimer was tapped by Lucy's discoverer, Donald Johanson, to analyze the foot bones of the afarensis species. Latimer is a widely known expert in the bio-mechanics and evolution of upright walking.

Haile-Selassie, an Ethiopian native, is a methodical scientist with an uncanny instinct for unearthing blockbuster fossils. They include the first bones of a substantially complete 4.4 million year old skeleton nicknamed "Ardi" – an early human ancestor from the species Ardipithecus ramidus.

An analysis of Ardi's remains, co-authored by Haile-Selassie, Latimer and others, created a worldwide sensation upon publication in 2009, when it revealed the earliest unambiguous evidence of upright walking.

Like the newly-discovered Burtele foot, Ardi's foot was a blend of primitive and modern features, including the grasping big toe for tree-climbing and four toes modified for upright ground-walking.

When Haile-Selassie first showed Latimer a plaster copy of the Burtele foot, "I said, 'You found another Ardi. Great!'" Latimer recalled in an interview. Then Haile-Selassie told his colleague that the primitive-footed Burtele fossils were 3.4 million years old – the same age as the modern-footed Lucy and afarensis. "I said it can't be," Latimer said. "Your brain doesn't want to go there."

Haile-Selassie and Latimer now suspect that the Ardipithecus lineage survived longer than scientists previously thought, lingering as a "relic" for several hundred thousand years even after Lucy's species, Australopithecus afarensis, branched off on its modern-walking trajectory.

"An ancestor species and its daughter species, descendant species, can overlap in time," Haile-Selassie said. "So this partial foot could belong to something like Ardipithecus that just persisted, being isolated in its own habitat, without losing its ability to climb trees. Whereas afarensis has already abandoned its use of trees as part of its habitat."

There's no way to confirm the Burtele foot is from the same evolutionary grouping as Ardi and its descendants without telltale "diagnostic" skull bones and teeth. Scientists rely on those, rather than skeletal bones, for precise genus and species identification. (The fossils don't contain DNA, ruling out genetic analysis.)

After Stanford University graduate student Stephanie Melillo spotted the first Burtele foot bone poking from a sandstone hillside on Feb. 15, 2009, she and the other expedition members gingerly hand-scraped the dusty ground and recovered the seven other forefoot fossils by day's end. But the search for other parts of the creature, particularly its head and jaws, proved fruitless.

View full sizeCourtesy Yohannes Haile-Selassie, CMNHProject member Stephanie Melillo holds the fourth metatarsal bone of the Burtele foot, which she found after erosion had uncovered the pieces.

Finding any intact fossil foot bones at all is extraordinary good luck; they're small and fragile, readily chewed up by predators or ground to dust by the shifting earth. None has been retrieved from Australopithecus anamensis, a 4.2 million-year-old human ancestor younger than Ardi but that pre-dates Lucy's species, leaving its locomotion a mystery.

"Recovery of any associated foot bones is obviously significant, given the fact that we find so few of them," said renowned University of California, Berkeley paleoanthropologist Tim White, the leader of the Ardi analysis and a frequent collaborator with Haile-Selassie and Latimer, but who was not involved in the Burtele discovery. "In this case, the elements they recovered reveal quite a bit about that foot's function."

Researchers know that afarensis' modern foot anatomy and fully-upright walking style date back to at least 3.6 million years ago. That's the age of a famous set of imprints called the Laetoli footprints, preserved in volcanic ash from Tanzania, that show a human-like, non-grasping big toe and a shock-absorbing arch from ball to heel.

The Burtele foot, which at 3.4 million years is "younger" and more recent than the Laetoli impressions made by Lucy's species, retained the big toe but lacked the arch. Its toe length proportions were gorilla-like, suggesting to Haile-Selassie that gorillas, not chimpanzees, are a better model for our earliest ancestor.

Latimer said he was surprised that the anatomical changes necessary for modern-style walking didn't happen all together in the Burtele creature's lineage. "The lateral side of the foot adapted first to bipedality, and the big toe came later," he said. "I would have thought it came as a package, but I was wrong."

View full sizeCourtesy Yohannes Haile-Selassie, CMNHThe bones of the Burtele forefoot are shown in the outline of a gorilla's foot. The proportions of the second and fourth metatarsal bones are gorilla-like, suggesting gorillas as a good model for the earliest human ancestor, says Yohannes Haile-Selassie.

This less-than-ideal evolutionary compromise enabled the Burtele creature to keep a literal toehold in its shrinking forest habitat, but prevented it from making a full transition to the ground, as Lucy and her kin already had done.

"When you're 60 feet up in the [tree] canopy and you slip, it's 'Goodnight, Irene,'" Latimer said. "So you've got to have" the grasping big toe. The Burtele hominin "probably was doing fine in the trees, but when it came down to the ground, it's probably going to be staggering. And the trees eventually are going to go away, and that's the end of it."

Though the area is a harsh wasteland today, sediment samples from the Burtele hominin's time show a range of conditions, from woodlands to a mix of trees and bushes lining river banks, said CWRU geologist Beverly Saylor, a co-author of the report. There were lakes and waterways teeming with fish, crocodiles and turtles, judging by the fossil remains.

Earth's warming, drying climate eventually wiped out the woods where the Burtele hominin dwelled. But habitat change alone probably is too simplistic an explanation for why the lineage petered out, while Lucy's species persisted until at least 2.9 million years ago and potentially led to our own.

Upright walking gave afarensis the mobility to explore different habitats and freed its hands to carry food. Its strong jaw muscles and thick teeth broadened its dietary choices to include tougher meals, not just the soft fruits in the dwindling forests.

Plaster copies of the Burtele foot bones eventually will go on display at the Cleveland Museum of Natural History, sharing the spotlight with the reproduction of Lucy's skeleton. The original foot fossils are the property of Ethiopia's National Museum, though Haile-Selassie said he plans to temporarily bring them to the United States for advanced X ray-scanning.

The Cleveland team will resume its Ethiopian fossil-hunting next year, hoping to explore sites considerably older than Burtele that may hold more ancient clues to bipedality's – and humanity's – beginnings.

Follow Us

cleveland.com is powered by Plain Dealer Publishing Co. and Northeast Ohio Media Group. All rights reserved (About Us).The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of Northeast Ohio Media Group LLC.